Chemically tuned nitrogen-doped sulfur host for a reversible and stable room-temperature sodium-sulfur batteries

Abstract

The fast transition of long-chain polysulfide to short-chain polysulfide causes a sharp decay in the performance of room-temperature sodium sulfur (RT-Na/S) batteries. The nitrogen-doped sulfur host is identified as effective in slowing the transition process by entrapping the sodium polysulfide. However, precise control over the amount of nitrogen remained a challenge. We report a chemical route to fine-tune nitrogen doping in the sulfur host. The nitrogen content in the sulfur host is identified to vary from 7 to 19 at. % by varying the reaction time from 4 to 12 h. The optimized reaction time of about 8 h results in the highest pyridinic and pyrrolic nitrogen content. In addition to nitrogen doping, the sulfur host with a hierarchical pore structure could be achieved with 8 h of reaction time. The as-developed sulfur host serves as a sulfur cathode and is used to fabricate an RT-Na/S battery. The cell could function stably for over 500 cycles at 1C, with a high Coulombic efficiency of ~99.5 % and a capacity decay of 0.28 mAh g−1 per cycle at 1C. The cell could function reversibly and stably at various C-rates (0.2C – 2C). This study paves a path for the researcher to revisit the design of the sulfur host to construct a stable cathode for RT-Na/S batteries.